The present invention relates to a foam-suppressing composition or, more particularly, to a novel silicone-based foam-suppressing composition in the form of an oil compound suitable for use in various kinds of foaming systems even under vigorous agitation.
It is a well established technology that silicone-based foam-suppressing compositions or defoaming agents are widely used for reducing disadvantages caused by foaming in an aqueous system in a variety of industrial fields including chemical industries, food industries, petroleum industries, fabric industries and pharmaceutical industries by virtue of their excellent defoaming activity as compared with defoaming agents of other types. Silicone-based defoaming agents are used in the form of an oil compound prepared by blending a silicone oil, such as a dimethyl polysiloxane, methyl phenyl polysiloxane and methyl vinyl polysiloxane, and a finely divided silica powder or in the form of an aqueous emulsion obtained by dispersing and emulsifying the above mentioned oil compound in an aqueous medium containing a surface active agent as an emulsifying agent. A problem in such an emulsion-type silicone-based defoaming agent is that the defoaming activity thereof is greatly decreased when the aqueous foaming liquid is at a high temperature, when the aqueous foaming liquid is strongly alkaline or when the foaming liquid is under vigorous agitation with a strong shearing force because the emulsion of the defoaming agent is destroyed under these adverse conditions. As a remedy for this problem, a proposal is made in Japanese Patent Publications 52-19836, 52-22638 and 55-23084 for a self-emulsifiable defoaming agent by the combined use of a silicone-based oil compound and an organopolysiloxane modified by polyoxyalkylene groups, which is suitable for use in dyeing processes of fabric materials and as an additive in various kinds of oiling agents and water-base inks.
The above mentioned improved silicone-based defoaming agents, however, are still not quite satisfactory due to the relatively low sustainability of the defoaming activity thereof especially when the defoaming agent is brought violently into contact with the foaming gas in a foaming liquid under vigorous agitation or when the foaming liquid is at a high temperature as is sometimes the case in the dyeing process of fabric materials. This problem can be solved only by increasing the amount of the defoaming agent added to the foaming liquid or by supplementarilyadding the defoaming agent in portions to compensate the decrease in the defoaming activity.
In view of the above described problems, other measures for the improvement of a silicone-based defoaming agent are proposed In Japanese Patent Publication 52-31836 according to which the silica powder compounded in an oil compound is rendered hydrophobic beforehand by a treatment with an organosilane compound such as dimethyl dichlorosilane and in Japanese Patent Publication 51-35556 according to which the silica powder is treated with a nitrogen-containing organosilicon compound such as hexamethyl disilazane. These methods are, however, not practical due to the lengthy treatment time for the hydrophobilizing treatment of the silica powder and complexity of the process as well as the costs for the apparatuses used in the hydrophobilizing treatment of the silica powder.
Further, Japanese Patent Kokai 57-48307 discloses a silicone-based defoaming agent which comprises an organopolysiloxane or a hydrocarbon compound with admixture of an organohydrogen polysiloxane, a silica powder and an organometallic compound as a catalyst. Such a composition is disadvantageous because the preparation procedure thereof involves a heat treatment of the composition after admixture of the catalyst in order to promote the surface treatment of the silica particles as well as a danger of explosion due to evolution of hydrogen gas. Japanese Patent Publication 3-39722 discloses a method in which an organopolysiloxane is admixed with an organosilicon compound and a catalyst and then subjected to a heat treatment. U.S. Pat. No. 4,486,336 discloses a defoaming agent comprising an organopolysiloxane, a silica powder and an organopolysiloxane resin consisting of (CH.sub.3).sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units. Japanese Patent Kokai 6-154513 discloses a method in which the silica powder as an ingredient of a defoaming agent is subjected to a treatment with a cyclic organosiloxane oligomer and a mixture of water and a reaction promoter. These methods or defoaming agents are, however, still not quite satisfactory in respect of the sustainability of the defoaming activity.
The inventors have continued extensive investigations with an object to obtain a silicone-based defoaming agent capable of exhibiting high defoaming activity with sustainability even at a high temperature and under a high shearing force. They have made several proposals including a method for the preparation of a defoaming agent in which an organopolysiloxane is compounded with a silica powder after a hydrophobilizing treatment and an inorganic ammonium salt and subjected to a heat treatment (Japanese Patent Publication 4-42043), an oil compound as a defoaming agent comprising a silicone oil having branched organosiloxane units and a silica powder (Japanese Patent Kokai 6-142411) and a method for the preparation of a defoaming agent in which an organopolysiloxane is compounded with a silica powder and a dispersing aid which is an inorganic or organic acid and subjected to a heat treatment. These proposals are in fact effective in obtaining a silicone-based defoaming agent having excellent sustainability of the defoaming activity but it is still desirable to develop a defoaming agent with further improvements in respect of the stability of the emulsion by dilution and under a strong mechanical shearing force.